Preparation of grease thickeners by alkali fusion of polyvinyl esters



PREPARATION OF GREASE THIGKENERS BY ALKALIFUSIGN 0F POLYVINYL EST ERS Jelfrey H. Bartlett, Westfield, and Arnold J. Morway, Rahway, N. 3;, assignors to E'sso Research and Engineering Company, a corporation of Delaware Nu Drawing. Application December 17,1953, Serial No. 398,857

is Claims. (Cl. 252-41 The present invention relatesto animproved method. of preparing lubricating greases andto grease compositions produced by this method. More specifically, the invention pertains to improvements in the manufacture; of grease thickeners and to greases containing such thickeners.

in brief compass, the invention. provides for making grease thickeners by a process involving treating polyvinyl esters with caustic alkali under fusion. conditions producing a metal soap from the acidic material soformed and incorporating this metal soap into a lubricating oil in grease-rnaking proportions. in a preferred embodiment of the invention, the. fusion is carried. out in a lubricating oil in the presence of preformed soaps of other carboxylic acids.

Lubricating greases normally consist. of lubricating oils thickened by alkali and alkaline earth metal. soaps or other thickeners to a solid or semi-solid consistency. The

soaps may be prepared by the neutralization of high molecular weight fatty acids or by the saponification of fats which is usually carried out in a portion of the. oil to be thickened. Saponification of fats has been the preferred grease-making method theretofore chiefly because greases produced in the absence of glycerine or similar materials have tendencies to become crumbly, to sweat oil and to break down into soft granular masses of reduced lubricating value. More recently, fatty acids are being frequently employed in combination with the gl-ycerides for various purposes, such as improvements in structure of the grease, its high temperature characteristics, etc.

The present invention pertains to highly valuable stable lubricating greases in which the high molecular weight hired States Patent 9 2 fatty acids are replaced or at least supplemented bya new= grease-making material. It has now been found that; such greases may be prepared by incorporating into lubri.- eating oils a grease thickener containing a material ob tained by treating polyvinyl esters with alkali under fusion; conditions, particularly caustic soda or potash at temperatures between 400 and 600 F., usually between about 480 and 580 F., for a time sufiicient toform the alkali metal salt of the acidic material produced by fusion, of: reactive hydroxyl groups, i. e. until gas evolution atleast begins to recede appreciably and, preferably, until' gas evolution substantially ceases.

Previous work described in. our copending application, Serial No. 325,444, filed December 11, 1952, has shown that cellulose and other high molecular weight polyhyd'ric compounds may be subjected to alkali fusion to form soap-type grease thickeners valuable in the manufacture of lubricating greases. However, attempts at utilizingpolyvinyl alcohols in a similar manner proved unsuccessful and no satisfactory greases could be formed. On the other hand, it has now been. found that high quality greases may be formed by subjecting polyvinyl esters to conditions conducive to. alkali fusion.

in accordance with the present invention, the polyvinyl esters are heated in the presence of caustic alkali at cone ditions adapted partially or completely to-hydrolyze the ester to the polyvinyl alcohol and to convert an oxygenated terminal carbon of the polyvinyl chain to a neutralized carboxylic acid group by caustic fusion. While it is not intended to limit the invention to any particular theory or reaction mechanism, it is noted that primary alcohol esters hydrolyze more readily than secondary alcohol esters. Hence it is possible that the terminal primary alcohol ester group on the polyvinyl ester is the first to hydrolyze and is partially or completely fused to the acid during the hydrolysis of the remaining secondary alcohol ester groups, provided suitable high temperatures; are used, It is also possible that some of the secondary alco-. hol groups are dehydrated during the fusion process, thus producing high molecular Weight unsaturated acids. Since there are so many competing reactions during the hydrolysis and: caustic fusion of the polyvinyl esters, it is believed that the compounds formed have a. long straight chain carrying ester groups, hydroxyl groups, olelinic groups and carboxylic acid salt or soap groups, as illustrated by the following theoretical equations:

A- -onl+onr and/or sodium acetate hydrogen and/ or 4- sodium acetate water hydrogen and/ or flsodium acetate 4 water hydrogen wherein A is the rest of the polymer molecule and x and y are indicators determining the chain length of the molecule. The relative position of the hydrolyzed, nonhydrolyzed and olefinic groupings within the molecule may, of course, be different from that shown above, the foregoing equation illustrating merely a random distribu tion. The basic reaction involved in alkali fusion of primary alcohol groups and their equivalents may be illustrated by the following equations:

RCHzOH-l-NaOl-Ie RCOONa+ 2H2 The discovery of the utility of alkali fusion of polyvinyl esters for grease making greatly increases the wealth of raw materials available for grease production. Heretofore, ester-type fats, oils or high molecular weight fatty acids have been used in the manufacture of soap-thickened greases and these starting materials have been believed almost indispensable for the purpose. All these materials have numerous other industrial uses, a situation condllcive to the development of shortages forcing frequent variations in grease-making procedures and grease characteristics. The discovery of an entirely new and plentiful class of grease-making raw materials eases this situation considerably.

The use of polyvinyl esters as grease-making materials introduces no complication into the grease-making procedure. The greases may be produced essentially in a single process step in which the polyvinyl ester is subjected to alkali fusion conditions in the lubricating oil base at grease-making conditions, although at somewhat higher temperatures. At the conclusion of the fusion process a finished grease is obtained.

Quite generally, the polyvinyl esters used should have at least about 24 carbon atoms per molecule or a molecular weight of about 1000200,000, preferably about 50,000l25,000.

In general, polyvinyl acetate is the most desirable of the polyvinyl esters because of its low cost and also because of the value of the acetic acid or sodium acetate obtained during hydrolysis as an important complexforming constituent of the grease thickener. Similar results may be obtained when using polyvinyl esters of other low molecular weight carboxylic acids, such as propionic, butyric, caprylic acids, etc. Also polyvinyl esters of high molecular weight carboxylic acids, such as decanoic, lauric, stearic, hydroxy stearic, oleic acids, etc., may be used for some purposes. Another important type of polyvinyl ester is the copolymer of vinyl acetate or other low molecular weight vinyl esters with vinyl esters of high molecular weight carboxylic acids, such as vinyl palmitate, vinyl stearate, vinyl coconate, caprylate, etc.

When carrying out the alkali fusion reaction in the lubricating oil itself so as to form the grease thickening soap in situ in accordance with the preferred embodiment of the invention, it has been observed that the alkali has a strong tendency to settle out of the reaction mixture to the bottom of the reactor in the form of a cake which does not fully participate in the reaction. Highly efficient stirring or agitation will counteract this tendency. However, in many cases more efficient stirring is required than may be obtained in conventional grease kettles and special equipment would have to be used.

It has now further been found that the settling tendency of the alkali in the lubricating oil-alcohol mixture is negligible when a sufficient amount of a solid suspending agent is present in the reaction mixture. Most desirable suspending agents are those which serve simultaneously as grease thickeners, such as soaps of high molecular weight fatty acids, silica gel, carbon black, bentones, Attapulgus clay modifications, etc.

Soaps, particularly sodium soaps of high molecular weight fatty acids, are preferred for this purpose. When higher melting point soap-type dispersing agents are desired the salt, preferably the alkali metal salt, of a low molecular weight acid may be used in addition to the high molecular weight fatty acid soap. In this manner, soap-salt complexes are formed which melt well above 500 F. and thus form an excellent suspending agent.

These soaps or soap-salt complexes are preferably formed in situ by neutralization of the corresponding acids in the polyvinyl ester-oil mixture with alkali added in amounts sufficient for this neutralization and the subsequent fusion which takes place at considerably higher temperatures. High molecular weight acids useful for this purpose include hydrogenated fish oil acids, C12-C22 naturally occurring acids of animal or vegetable origin,

etc. These acids may be .used in amounts ranging from about 2-30 wt. percent based on the finished product. Suitable low molecular weight acids include carboxylic acids having 15 carbon atoms per molecule, such as formic, acetic, furoic, arcylic and similar acids to be used in proportions of about 1-10 wt. percent based on the finished product. Esters of the high and/or low molecular weight acids, particularly those containing mono basic acid esters may be used in place of the free acids in corresponding proportions. In this case, the alcohol portions of the esters are converted into acids and the corresponding soaps by alkali fusion. If esters of low molecular weight alchols are used, elevated pressures may be employed to prevent volatilization of the alcohols. Of course, esters of non-volatile low molecular weight alcohols, such as polyhydroxy alcohol esters, e. g. sorbitol acetate, glycol acetate, etc. may be used. When polyvinyl acetate or other polyvinyl esters with low molecular weight acids are used as the principal starting material, the amount of low molecular weight acid introduced in this manner may be sufiicient for the desired complex formation. The high molecular weight type of acids or their esters used for this purpose may also be prepared by alkali fusion of 0x0 products.

Soaps of high molecular weight fatty acids and particularly soap-salt complexes of the type specified may be incorporated in the greases of the present invention to improve high temperature or other characteristics even if no suspending agents are required. Thus, it has been found that the use of soaps derived from polyvinyl esters as the sole grease thickeners often tend to be relatively less stable to mechanical working and have dropping points below 400 P. which may be undesirable. However, when these polyvinyl ester soaps are mixed with soaps derived from fatty acids, this is largely eliminated or modified to an extent that is desirable for certain purposes.

In accordance with a specific modification of this embodiment of the invention, polyvinyl acetate of about 50,000-l25,000 molecular weight is employed to produce the major portion of the soap thickener, preferably in the presence of other high molecular weight fatty acids. On hydrolysis and fusion of the polyvinyl acetate with alkali the soap product described above is formed along with alkali metal acetate. This combination of the alkali metal soaps formed by fusion of the OH groupings and the alkali metal acetate may be employed as a thickener for lubricating grease. Other low molecular weight aliphatic acids may be used in place of acetic acid although this acid is preferable in this modification of the invention.

The soaps formed by alkali fusion of polyvinyl esters -in the presence of other fatty acid soaps consistently yield excellent smooth greases. Other conventional thickeners, antioxidants, corrosion inhibitors, tackiness agents, loadcarrying compounds, viscosity index improvers, oiliness agents and the like may be added prior, during and/ or after the fusion process as will be apparent to those skilled in the art.

The base oil used as menstruum during the fusion process should be non-saponifiable at the fusion conditions and is preferably a hydrocarbon oil, particularly a mineral lubricating oil. However, other hydrocarbon lubricating oils, such as olefin polymer oils, alkylated naphthalene oils, etc., non-hydrocarbon oils such as formals, acetals, mercaptals, silicone oils and certain other synthetic oils of lubricating grade may be used. After fusion is completed, the same or other oils may be added, for example, synthetic lubricating oils, such as a dibasic acid ester (e. g. di-2-ethyl hexyl sebacate, adipate, etc.), polyglycol type synthetic oils, esters of dibasic acids and polyhydric alcohols, etc., as well as alkyl silicates, carbonates, phosphates, etc., may be used alone or in addition to mineral or other non-saponifiable lubricating oil to bring the grease to the desired consistency. The oil base preferably comprises about 50 to about 95% of the total weight of the finished grease.

As indicated above, the process of the invention may be carried out in two stages. When so operating, the polyvinyl ester to be fused may be added over a period of several hours, say 3 hours to a molten mixture of alkali and non-saponifiable oil, preferably a heavy mineral oil, maintained at fusion temperatures of, say, about 530- 580 F. The proportion of alkali used may amount to about -50 Wt. percent, preferably about -40' wt. percent of the polyvinyl ester, calculated as NaOH. When all the polyvinyl ester has been added, heating may be continued at these temperatures to complete the reaction, as indicated by a cessation of gas evolution.

The soaps so prepared may then be introduced into a lubricating oil base stock. Other high and/or loW molecular Weight fatty acids as well as other grease additives may be added and the mixture may be converted into a grease by the addition of at least sufiicient caustic alkali to neutralize the acids present. Conventional greasemaking conditions including temperatures of about 350- 500 F. may be used in this stage. The soaps derived from the polyvinyl acetate by alkali fusion should form at least 20 wt. percent and preferably about -60 wt. percent of the grease thickener or about 2.0-20 Wt. percent of the finished grease. The remainder of the grease thickener is preferably made up by a suitable soap or soap-salt complex of the type described above. The proportion of soap derived from polyvinyl ester to soaps and salts derived from other acids may be about 1:4 to 4:1 and preferably is about 1:1.

In order to prepare a grease by alkali fusion in situ in accordance with a more desirable embodiment of the invention, the grease-making procedure may be quite generally as follows. A non-saponifiable, preferably mineral lubricating oil base is mixed with the polyvinyl acetate and alkali, preferably in aqueous solution, at temperatures not substantially exceeding 150 F. The mixture is heated to about 350400 F. When dehydration is complete the temperature is raised to about 480-600 R, preferably about 530580 F. Heating at these temperatures is continued until the desired conversion has been obtained, which is usually the case after about 0.5-5 hours. The reaction mixture is quenched or allowed to cool and may then be diluted with further amounts of lubricating oil to the desired grease consistency.

A similar procedure is employed when the polyvinyl ester is subjected to alkali fusion in situ in the presence of suspending agents, such as soaps of high molecular weight fatty acids or complexes of such soaps with low molecular weight fatty acid salts in accordance with the preferred embodiment of the invention. In this case, all the acids needed to form the suspending agents are added to the mixture of polyvinyl ester, alkali and mineral oil. Sufiicient caustic alkali is used to neutralize these acids and to supply additional alkali amounting to about 10-50 wt. percent, preferably about 25-40 wt. percent of the polyvinyl ester used. The caustic alkali is preferably employed in the form of an aqueous solution of about 15-30%. The mixture is heated at a saponification temperature of about 300-400 F. until the acids are converted to soaps and salts and all the water is volatilized.

Example I A grease was prepared from the following ingredients:

Ingredients Weight. percent Polyvinyl acetate 11.5 Hydrofol Acids 51 10.3 Sodium hydroxide 6.7

Phenyl alpha-naphthylaminenu 1.2

Naphthenic-type mineral oil having a viscosity of 50 SSU at 210 F 70.2

Dupont Elvacet aqueous emulsion 55% minimum solids.

(Used 405 grams of emulsion.) Molecular weight approximately 125,000.

Hyd rogenated fish oil acids corresponding to commercial stearic acid in degree of saturation.

Pre'para'zio'n .The vinyl acetate emulsion, /2 of the mineral oil and the Hydrofol acids were charged to a fire heated grease kettle equipped with eflicient stirring. The mass was heated to 150 F. Then the sodium hydroxide was added as a 40% aqueous solution. Heating was continued slowly to 400 F. until all the water was removed. Thereafter the balance of the mineral oil was added and the mixture was heated to 570 F. as follows:

Elapsed time, minutes: Temp., F.

-L---- 15 r 500 40 a 550 60 1 570 115 200 1 Shut off heat and added phenyl alphanaphthylamine.

The cooled product was homogenized in a Gaulin. homogenizer at 3,000 p. s. i.

Properties (after Gaulin homogenization):

Worked, 100,000 strokes 220. Water washing test, percent loss None. Norma Hoffman oxidation test, hours to 5 p. s. i. drop in oxygen pressure 274.

Example I] The grease of Example I was diluted with by weight of a high viscosity index type mineral lubricating oil.

Weight percent Grease base (Example I) 50 Solvent extracted Mid-Continent mineral oil distillate (vis. 57 SSU at 210 F.; 102 V. I.) 50

The oil and the grease base were mixed together cold in a Hobart mixer and then Gaulin homogenized. The finished grease had the composition and properties listed below.

Formulation: Weight percent Polyvinyl acetate; 5.75 Hydrofol Acids 51 5.15 Sodium hydroxide i 3.35 Phenyl alpha-naphthylamine 0.60 Mineral oil having a viscosity of 55 SSU at 210 5 F. 85.1

Properties:

Appearance "Excellent smooth grease. Penetrations, 77 F., mm./

Unworked 339.

Worked, 60 strokes 358. Worked, 80,000

- strokes Semi-fluid. Water washing test, percent loss 5. Dropping point, "P 440.

Oxidation, hours to 5 p. s.

i. drop in Oz pressure 235. Wheel hearing test, 6

slight tendency to thin out with increasing temperature up to its melting or dropping point. Lubrication life, hours at 10,000 R. P. M. and 250'F 784.

The invention is not limited to the specific figures of the foregoing examples. The relative proportions of the grease constituents may be varied within the limits indicated above to obtain greases of different consistency and varying characteristics.

What is claimed is: H

l. A grease thickener comprising a metal soap material produced by reacting a polyvinyl ester having a molecular Weight of about 1,000200,000 with an alkali metal hydroxide at conditions including a temperature in the range of 480 to 600 F. conducive to alkali fusion at least until substantial amounts of hydrogen have been liberated.

2. A lubricating grease comprising a major proportion of a lubricating oil and a minor grease-making proportion of a grease thickener containing at least 20 wt. percent of a metal soap material produced by reacting a polyvinyl ester having a moleuclar weight of about 1,000200,000 with an alkali metal hydroxide at conditions conductive to alkali fusion including a temperature in the range of 480 to 600 F.

3. The grease of claim 2 in which said ester is polyvinyl acetate having a molecular weight of 50,000- 125,000.

4. The grease of claim 2 in which said ester comprises a polyvinyl ester of a low molecular weight carboxylic acid.

5. The grease of claim 2 in which said ester comprises a polyvinyl ester of a high molecular weight carboxylic acid.

6. The grease of claim 2 in which said lubricating oil comprises a mineral oil.

7. The grease of claim 2 in which said polyvinyl ester is polyvinyl acetate.

8. A lubricating grease comprising a major proportion of a lubricating oil and a minor grease-making proportion of a grease thickener containing at least 20 wt. percent of a metal soap material produced by subjecting an alkali metal hydroxide and a polyvinyl ester having a molecular weight of about 1,000200,000 to conditions conducive to alkali fusion including a temperature in the range of 480 to 600 F. and a substantial proportion of an'alkali metal soap of a high molecular weight fatty acid other than acid derived from said ester by said fusion,.the fatty acid soap being present in an amount ranging from 2 to 30 wt. percent, and the metal soap derived from said ester being present in an amount in the range of 2 to 20 wt. percent, based on final composition.

9. The grease of claim 8 which contains in addition to said material a substantial proportion of a complex of a high molecular weight fatty acid alkali metal soap with a low molecular weight fatty acid alkali metal salt.

10. The process of preparing lubricating greases which comprises contacting a polyvinyl ester having a molecular weight of about LOGO-200,000 with an alkali metal hydroxide at conditions including a temperature in the range of 480 to 600 F. conducive to alkali fusion, producing a metal soap from the acidic material so formed and incorporating said soap into a lubricating oil in grease making proportions, said soap amounting to 2-20 wt. percent of the final grease composition.

11. The process of claim 10 in which said fusion is carried out in a suspending proportion of said lubricating oil, said oil being non-saponifiable at said conditions.

12. The process of preparing lubricating greases which comprises contacting a polyvinyl ester having a molecular weight of about 1,000200,000 with an alkali metal hydroxide at conditions including a temperature in the range of 480 to 600 F. conducive to alkali fusion in the presence of a preformed alkali metal soap of a high molecular weight fatty acid at least until substantial amounts of hydrogen have been liberated, producing a metal soap material from the acidic material formed by fusion and incorporating said soap and material into a lubricating oil in grease making proportions, said soap amounting to 2-30 wt. percent and said material amounting to 220 wt. percent of the final grease composition.

13. The process of claim 12 in which said preformed soap is present in the form of a complex with 1 to 10 wt. percent, based on final grease composition, of the alkali metal salt of a low molecular weight carboxylic acid.

14. A lubricating grease comprising a major proportion of a mineral lubricating oil and a minor greasemaking proportion of a grease thickener consisting essentially of a sodium soap of a high molecular weight fatty acid and the soap material obtained by contacting polyvinyl acetate of about 125,000 molecular Weight with sodium hydroxide at temperatures of 480570 F. for about 1 hour.

15. The process of preparing a lubricating grease which comprises mixing a major proportion of mineral lubricating oil with a minor proportion of a high molecular weight fatty acid and a minor proportion of polyvinyl acetate of about 125,000 molecular weight, heating the mixture to a temperature not substantially exceeding about F, adding an aqueous solution of sodium hydroxide in amounts suflicient to neutralize said acid and to convert polyvinyl acetate into metal soap material, thereafter heating slowly to about 300400 F., adding further mineral lubricating oil, heating the mixture to about 570 F. within about 1 hour and cooling the mixture said neutralized fatty acid and metal soap material bei'ngsufiicient to thicken the mineral lubricating oil to grease consistency. Y

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ralston: Fatty-Acids and Their Derivatives, page 737, Wiley, 1948. 

12. DTHE PROCESS OF PREPARING LUBRICATING GREASES WHICH COMPRISES CONTACTING A POLYVINYL ESTER HAVING A MOLECULAR WEIGHT OF ABOUT 1,000-200,000 WITH AN ALKALI METAL HYDROXIDE AT CONDITIONS INCLUDING A TEMPERATURE IN THE RANGE OF 480* TO 600* F. CONDUCIVE TO ALKALI FUSION IN THE PRESENCE OF A PREFORMED ALKALI METAL SOAP OF A HIGH MOLECULAR WEIGHT FATTY ACID AT LEAST UNTIL SUBSTANTIAL AMOUNTS OF HYDROGEN HAVE BEEN LIBERATED, PRODUCING A METAL SOAP MATERIAL FROM THE ACIDIC MATERIAL FORMED BY FUSION AND INCORPORATING SAID SOAP AND MATERIAL INTO A LUBRICATING OIL IN GREASE MAKING PROPORTIONS, SAID SOAP AMOUNTING TO 2-30WT. PERCENT AND SAID MATERIAL AMOUNTING TO 2-20 WT. PERCENT OF THE FINAL GREASE COMPOSITION. 